Elucidating how particle packing controls rheology and strength development of dense cementitious suspensions

Although maximizing particle packing strategy is primarily applied to formulate high performance cementitious suspensions, this may induce constraints for the growth of hydration products, resulting in reduced microstructural evolution at later ages. This paper elucidates the effects of particle packing on rheology and strength development of dense suspensions containing ordinary portland cement (OPC) and supplementary cementitious materials (SCMs). The particle packing was altered through tuning water film thickness to examine its impact over transition of cementitious suspensions from concentrated state to the onset of flow state. This transition was characterized by determining the optimum water demand to achieve maximum solid concentration and minimum water demand to initiate flow. A series of virtual microstructural simulations were also performed to examine the effect of excess water on inter-particle spacing and formation of the connected solid network through formation of main cement hydrate (i.e., calcium-silicate-hydrate (C-S-H)). The results indicate that although transition of the cementitious suspension from concentrated state to the onset of flow state reduces particle packing and elevates separation between neighboring particles, these effects become less pronounced for the OPC-SCM systems than the plain OPC system. The synergistic effect between OPC and SCMs on strength development is controlled by water extent. An account of saturated surface area effect, rate of strength evolution slows down at concentrated state. The outcomes of this study can be applied to optimize the design of dense cementitious suspensions by exploiting optimal particle packing while enabling strength development by providing pore space for growth of hydration compounds.